Increased levels of systemic iron content in adult-onset interleukin-6 knockout mice

Interleukin-6 (IL-6) is a pleiotropic cytokine that participates in multiple metabolic disorders. IL-6 is well recognized to induce hepcidin expression and decreased serum iron through the JAK2/STAT3 pathway under inflammatory conditions. Targeted inhibition of IL-6 represents a potential therapeutic regimen for multiple diseases. The current study aimed to explore the physiological concentration of IL-6 in sustaining systemic iron homeostasis.

IL-6-knockout mice (IL-6-/-) were established in the current study. Western blot measured the expression of key iron-related proteins in liver, kidney, spleen and duodenum, as well as hepatic hepcidin mRNA expression. Serum iron and hematologic parameters were detected. ELISA and Masson's trichrome staining were performed to detect renal TGF-β1 expression and collagen deposition. Furthermore, bone marrow-derived and peritoneal macrophages were prepared to identify the iron recycling.

Serum iron and tissue iron content were markedly elevated in IL-6-/- mice. Mechanistically, decreased renal erythropoietin (EPO) synthesis contributed to iron utilization, macrophage-mediated recycling of iron was markedly reduced, thereby resulting in systemic iron accumulation. However, IL-6-/- mice displayed increased Hepcidin expression via p-ERK activation and a significant reduction in duodenal iron uptake.

This study highlighted the critical role of IL-6 in iron homeostasis both in physiological and pathological situations.